An organic electroluminescent element (hereinafter, referred to as “organic EL element”) utilizing electroluminescence (hereinafter, referred to as “EL”) of an organic material is a thin-film type completely-solid state element capable of emitting light at a low voltage of several volts to several ten volts, and has many excellent features such as high luminance, high light emission efficiency, small thickness and light weight. Accordingly, in recent years, the element has attracted attention, as backlights for various kinds of displays, display boards such as a signboard and an emergency lamp, and surface emitting bodies such as illumination light sources.
Such an organic electroluminescent element has a configuration obtained by holding a light emitting layer formed of an organic material between two electrodes, the emitted light generated in the light emitting layer is extracted to the outside through the electrode. Therefore, at least one of the two electrodes is constituted as a transparent electrode.
As the transparent electrode, there is used generally a material of an oxide semiconductor type such as indium tin oxide (SnO2-In2O3:Indium Tin Oxide:ITO), and examination aiming at lowering electric resistance by laminating ITO and silver has been carried out (e.g. referring to the following Patent Literatures 1, 2). However, ITO has a high raw cost because of using a rare metal indium, and is required to be subjected to annealing treatment at about 300° C. after film formation in order to lower its electric resistance. Accordingly, there have been proposed a configuration in which a metallic material such as silver having a high electrical conductivity is made into a thin film, and a configuration in which an electrical conductivity is ensured even at a film thickness smaller than that of silver alone by blending aluminum with silver (for example, referring to the following Patent Literature 3).